Monetizing natural gas associated with remote oil production or stranded gas reserves having no access to distribution infrastructure presents enormous challenges. Flaring or venting of such “associated gas” is both wasteful and detrimental to the environment. It is often more desirable to convert the natural gas into higher molecular weight hydrocarbons at a remote location near the source than to transport the natural gas to another location for conversion.
Many processes, such as Fischer-Tropsch synthesis, can convert methane-derived synthesis gas, also referred to as syngas, to hydrocarbons having a higher molecular weight, e.g., in the wax range. Fischer-Tropsch synthesis involves a polymerization reaction beginning with a methylene intermediate to produce a wide distribution of hydrocarbons ranging from light gases to solid wax. The resulting higher molecular weight hydrocarbons are difficult to transport because they are solid at room temperature.
Since it is desirable to transport waxy petroleum crude and Fischer-Tropsch products from remote sites to distant commercial refineries, there have been attempts to develop acceptable approaches for this transportation. For instance, waxy crude oils are shipped in specially equipped crude carriers at temperatures up to around 160° F. (71° C.). Typical maximum temperatures for conventional crude carriers are 140° F. (60° C.). The use of conventional crude carriers, those that ship materials at temperatures at or below 140° F., is preferred whenever possible because these carriers have significantly lower operating costs. Transporting solids requires forming, loading, and unloading facilities and is thus difficult and expensive.
In order to economically monetize remote associated natural gas or stranded gas, it would be desirable to have a way to produce a Fischer-Tropsch product which is blendable with crude oil in a compact, modular unit capable of being placed on offshore production structures. Specifically, it would be desirable to produce a hydrocarbon product containing at least 50 wt % C5+ and less than 25 wt % C21+ hydrocarbons which is a pourable liquid and blendable with crude oil at room temperature at a C5+ productivity from 0.05 to 2 gC5+/gcat/h.